The present invention relates to multi-piece fasteners and more particularly to a high strength blind bolt of the threaded torque type for providing a high final clamp load of workpieces secured together. As noted in the above related patents and patent application such blind fasteners, while of general utility, can be particularly useful in constructions utilizing box beams or columns, bridges and the like and more particularly in applications where accessibility on one side of the workpiece is blocked or limited.
The fastener of the present invention also relates generally to multi-piece blind bolt fasteners which include a main sleeve, an expandable sleeve and a pin wherein the expandable sleeve is expanded radially to form a blind head in response to a relative axial force applied via the pin. In this regard the blind bolt of the present invention, in addition to the patents noted above, is generally related to threaded blind fasteners of the type shown in U.S. Pat. No. 3,643,544 issued Feb. 22, 1972 to Joseph H. Massa; fasteners of this type have been sold under the trade names Visu-Lok and/or Jo-Bolt by the Monogram Aerospace Fastener Company and Voi-Shan Manufacturing Company of the U.S. See also U.S. Pat. No. 3,262,353 issued Jul. 26, 1966 to R. Waeltz et al, U.S. Pat. No. 2,765,699 issued Oct. 9, 1956 to J. LaTorre, U.S. Pat. No. 2,887,003 issued May 19, 1959 to Brilmeyer and U.S. Pat. No. 3,107,572 issued Oct. 22, 1963 to Orloff. As noted in the related U.S. Pat. No. 5,213,460 the prior blind bolt fasteners have certain problems since the main sleeve can absorb a significant portion of the force available to develop the clamp load and in addition the clamp load, tensile strength and blind side protrusion can vary within the grip range of the fastener. In this regard the grip range of the fastener is defined by the difference between the maximum total thickness and the minimum total thickness of workpieces which can be secured together by a single fastener. In the present invention, however, a unique blind bolt construction is provided having a wide grip range capability and in which a high strength blind head of a uniform structure is formed over this wide grip range. Thus the blind head of uniform structure will have the same blind side protrusion over the grip range. In addition the present invention provides a structure in which high strength materials can be used resulting in a high strength fastener while at the same time achieving a high, uniform clamp force.
In the present invention, a threaded nut and core bolt or pin construction is used and, as such, a nut member is threadably engaged on a threaded portion of the shank of the pin. A splined portion is located at the terminal end of the pin shank. An installation tool has a central socket member adapted to engage the splined portion and an outer wrench member adapted to grip the nut whereby torque can be applied between the core bolt or pin and the nut to provide relative rotation by which the nut is threaded onto the pin to attain the desired clamp up. A pair of sleeves, an expandable sleeve and a main sleeve, located on the pin cooperate to form a blind head in response to the applied torque.
In the present invention, as a result of the applied torque between the nut and the pin, the nut initially transmits an axial force to the main sleeve via a grip adjuster. At the same time, the pin has an enlarged head which transmits an opposite axial force against the expandable sleeve. As the torque and resultant relative axial force increases, the expandable sleeve, reacting against the main sleeve, is radially expanded to form a blind head. As will be seen a blind head of uniform shape is provided over the extended grip range of the fastener.
In many cases, the conventional installation tools for TC type high tension bolts apply relative torque between the pin and nut whereby either can rotate relative to the other. In the event the pin is rotated relative to the nut the frictional engagement between the pin head and expandable sleeve could result in abrasion and unwanted wear and deformation of these components. This could adversely affect the formation and strength of the blind head. Such relative rotation is likely to occur where the pin and expandable sleeve are coated with an anti-corrosion coating. Such coatings frequently add lubricity to the engaging surfaces, reducing friction and thereby enhancing the likelihood of pin rotation. In the present invention, an anti-rotation structure is formed at the engaging surfaces between the pin head and the expandable sleeve whereby such relative rotation is inhibited.
At this stage of the installation the workpieces have not been subjected to any clamp loads between the nut and grip adjuster and the blind head via the pin. In order to bring the blind head into engagement with the blind side surface, the grip adjuster is provided with a frangible member which is in blocking communication with a cavity. The frangible member is adapted to fracture at a preselected magnitude of relative axial force whereby the cavity which is no longer blocked is now accessible permitting axial movement of the main sleeve away from or out of load bearing relationship with the expandable sleeve; this permits the fully formed blind head to be brought into contact with the blind side surface of the workpieces with no axial restraint from the main sleeve which has moved substantially freely out of load bearing engagement with the expandable sleeve. Now the workpieces are pulled together by the further application of torque with the resultant relative axial force acting substantially solely between the blind head through the pin and the nut. The force clamping the workpieces together continues to increase until a magnitude of torque is attained at which a splined, pintail portion on the core bolt or pin is fractured from the pin. This fracture load determines the final clamp load on the workpieces. In one form of the present invention the blind bolt employs a core bolt or pin having a splined end portion in which the spline crests are of generally the same diameter as the crests of the adjacent bolt threads; a continuous thread form extends across the splined portion and the threaded portion. By providing a pin with such a splined structure, a conventional double socket drive tool used for TC bolts can also be used for installing the noted blind torque type bolts for use in workpiece bores of the same diameter.
As will be seen, the grip adjuster can be of a relatively simple construction and can be made of a high strength material whereby the strength of the frangible resistance or shear portion can be set at a high level. In this regard, this relatively simple construction readily allows the load for shearing the frangible resistance portion to be set at a level high enough to guarantee formation of the blind head and low enough to fracture before attainment of the final torque load for final clamp and fracture of the breakneck.
In one form of the invention both the main and expandable sleeves can be of generally straight tubular constructions of generally uniform cross-sections, i.e. without any significant change of cross section along their lengths, and the blind head is formed, through column loading, after insertion into the workpiece openings, by bulbing a portion of the expandable sleeve which is located beyond the blind side of the workpieces. In this regard, this type of structure is generally of the kind shown in U.S. Pat. Nos. 2,061,628 and 2,026,629 issued Nov. 24, 1936 to Huck, U.S. Pat. No. 2,114,493 issued Apr. 19, 1938 to Huck and U.S. Pat. No. 2,527,307 issued Oct. 24, 1950 to Huck. Formation of the blind head at a preselected location can be facilitated by annealing a circular band on the expandable sleeve at the desired location. See in this regard U.S. Pat. No. 3,253,495 issued to Orloff on May 31, 1966. As will be seen the bulbed blind head can provide an enlarged bearing surface and hence be especially useful in applications in which the workpiece openings are substantially larger than the effective diameter of the fastener.
Another form of blind head frequently employed with blind fasteners is referred to as a tuliped blind head. An example of a blind head of a tulip shape is shown in the U.S. Pat. No. 3,136,204 issued Jun. 9, 1964 to P. J. Reynolds; see also U.S. Pat. No. 4,012,984 Issued Mar. 22, 1977 to Matuschek, U.S. Pat. No. 4,451,189 issued May 29, 1984 to Pratt and U.S. Pat. No. 4,627,775 issued Dec. 9, 1986 to Dixon. In one form of the invention where a blind tuliped head is formed, this is done by forming the blind head to have a final form including both bulbed and tuliped blind head constructions whereby the strength of the blind head is increased.
As noted with the fastener of the present invention, a unique construction is provided in which the final clamp load onto the workpieces is maximized and none is absorbed by the sleeve structure; at the same time the fastener can be provided with a determinable, wide grip range and the maximized final clamp load will be generally uniformly available over this wide grip range. As will be seen, one form of the present invention inhibits distortion of the expandable sleeve by providing a structure for controlling the magnitude of axial force applied to the expandable sleeve after the formation of the bulbed head but prior to fracturing the frangible resistance or shear member. Such distortion could result in a reduction in the final clamp load attained on the workpieces.
Features of the present invention can be utilized with fasteners having the blind head formed by radial expansion of an expandable sleeve by a tapered nose portion on a main sleeve member, see U.S. Pat. Nos. 5,178,502 and 5,213,460, supra.
Thus the high strength blind bolt of the present invention is readily adaptable for use in applications utilizing high strength bolts, such as those meeting ASTM A325 or Japanese J1SB1186/F8T specifications. It is also desirable for use where blind welding, nut plates and other complex construction fastening systems are used in such structural elements such as box beams where there is no access to the backside of the joint. In this regard, the blind fastener of the present invention is especially suited in the construction of buildings, bridges, and the like where high strength and durability are of considerable importance along with the capability of providing high clamp loads.
Thus it is an object of the present invention to provide a torque type threaded blind bolt construction facilitating the use of high strength materials resulting in a high strength fastener having a wide grip range.
It is another object of the present invention to provide a unique blind bolt construction for providing a blind head having a combined bulbed and tuliped formation.
It is another general object of the present invention to provide a unique torque type threaded blind bolt of a high strength construction and that forms a high strength blind head having a uniform, desired configuration over a wide grip range.
It is another general object of the present invention to provide a unique high strength blind bolt utilizing a torque type threaded construction and providing a generally uniform high final clamp load over a wide grip range.
It is still another object of the present invention to provide a unique torque type threaded fastener having a pin with an enlarged head engaging an expandable sleeve and including a construction for inhibiting relative rotation between the pin and the expandable sleeve.
Other objects, features and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, in which: